1. Field of the Invention
The present invention relates to a rotor structure for an AC generator or a motor and, particularly, to a structure for attaching magnets for preventing the leakage of a magnetic flux between claw-like magnetic poles.
2. Description of the Prior Art
FIG. 17 is a sectional side view of a prior art rotor structure for an AC generator or a motor, FIG. 18 is a perspective view of the rotor, and FIG. 20 is an exploded side view of individual parts of the rotor.
As shown in FIG. 17, this generator comprises a case 3 consisting of an aluminum front bracket 1 and an aluminum rear bracket 2, a shaft 6 which is installed in the case 2 and one end of which is fitted with a pulley 4, a Randle type rotor 7 fixed to the shaft 6, fans 5 fixed to both end surfaces of the rotor 7, a stator 8 fixed to the inner wall of the case 3, slip rings 9 which are fixed to the other end of the shaft 6 and supply a current to the rotor 7, a pair of brushes 10 in sliding contact with the slip rings 9, a brush holder 11 for storing the brushes 10, a rectifier 12 which is electrically connected to the stator 8 and rectifies an alternating current generated in the stator 8 into a direct current, a heat sink 19 attached to the brush holder 11, and a regulator 20 which is attached to the heat sink 19 and regulates an AC voltage generated in the stator 8.
The rotor 7 comprises a cylindrical rotor coil 13 for generating a magnetic flux with a current and a pole core 14 which covers the rotor coil 13 and forms a magnetic pole with the magnetic flux of the rotor coil 13.
The stator 8 comprises a stator core 15 and a stator coil 16 which is wound round the stator core 15 and generates an alternating current by a change in magnetic flux from the rotor coil 13 caused by the rotation of the rotor 7.
The pole core 14 consists of a first pole core body 21 and a second pole core body 22 which are mated with each other.
The pole core body 21 and the pole core body 22 are generally made from iron and consist of cylindrical portions 21e and 22e wound with the rotor coil 13 and disk-like base portions 21k and 22k from which the cylindrical portions 21e and 22e project, respectively. The base portions 21k and 22k have at the peripheries a plurality of claw-like magnetic poles 23 and 24 which are mated with each other between the outer wall of the rotor coil 13 and the inner wall of the stator 8, respectively.
The thickness and width of each of the claw-like magnetic poles 23 and 24 are large on the base portion 21k and 22k sides and become smaller toward the end sides.
The inner faces 23a and 24a of the claw-like magnetic poles 23 and 24 become thinner toward the ends and the outer faces 23b and 24b are arched in conformity with the inner wall of the stator 8. Each of the claw-like magnetic poles 23 and 24 has two trapezoidal side faces 23c and 24c in a circumferential direction of the rotor 7. Since each pair of claw-like magnetic poles 23 and 24 are mated with each other, the inner faces 23a and 24a of the claw-like magnetic poles 23 and 24 are arranged alternately in a circumferential direction. The side faces 23c and 24c of the claw-like magnetic poles 23 and 24 are inclined toward the centers of the claw-like magnetic poles 23 and 24 so that they become thinner from the root side toward the end side.
As shown in FIG. 18, a rectangular magnet 30A magnetized to suppress the leakage of a magnetic flux between the opposed side faces 23c and 24c is fixed between the adjacent claw-like magnetic poles 23 and 24.
A description is subsequently given of the operation of the generator. A current is supplied from an unshown battery to the rotor coil 13 through the brushes 10 and the slip rings 9 to generate a magnetic flux, whereby the claw-like magnetic poles 23 of the first pole core body 21 are magnetized to an N pole and the claw-like magnetic poles 24 of the second pole core body 22 are magnetized to an S pole. Meanwhile, the pulley 4 is turned by the rotation force of an engine and the rotor 7 is turned by the shaft 6, thereby generating electromotive force in the stator coil 16. This AC electromotive force is rectified into a direct current by the rectifier 12, regulated by the regulator 20 and charged into the unshown battery.
The above magnet 30A which is inserted between the claw-like magnetic poles 23 and 24 and is rectangular or may be various in shape, for example, ring-shaped or ring-shaped and packed in other resin is fixed to the claw-like magnetic poles 23 and 24 by fixing means.
However, the following problems may occur. That is, since stress is applied to the magnet 30A at the time of production or centrifugal force generated by rotation is applied to the magnet 30A, the magnet 30A is inferior in durability.
Further, since the pole core bodies 21 and 22 are generally produced by forging, details of the claw-like magnetic poles 23 and 24 which have a specially complex shape cannot have high accuracy. There are differences in size between the claw-like magnetic poles 23 and 24. It is difficult to manufacture the magnet 30A which is formed in conformity with the inner faces 23a and 24a of the claw-like magnetic poles 23 and 24 which differ from each other and a support member which is molded in conformity with the claw-like magnetic poles 23 and 24.
When the magnet 30A is manufactured in consideration of molding ease, it becomes fragile. Therefore, when it is installed near the claw-like magnetic poles 23 and 24 of the rotor 7, some measure is necessary. However, when the magnet 30A is made sufficiently thick or very strong, it costs dear, making it difficult to mass-produce it.
Suppose that the magnet 30A and the support member are produced in accordance with the differences and that differences in the gaps between the claw-like magnetic poles 23 and 24 and the magnet 30A and between the claw-like magnetic poles 23 and 24 and the support member are made small. Even if the differences are small, when the magnet 30A receives centrifugal force at the time of the rotation of the rotor 7, a great force difference is produced, thereby making it possible that the magnet 30A and the support member are damaged.
When the magnet 30A is supported by the side faces 23C and 24c of the claw-like magnetic poles 23 and 24 irrespective of the inner faces 23a and 24a of the claw-like magnetic poles 23 and 24, force may be applied to the magnet 30A by the dislocation of each of the two pole core bodies 21 and 22 when they are mated with each other or dislocation caused by rotation force.
The end portions of the claw-like magnetic poles 23 and 24 are moved toward the rotor coil 13 and the stator 8 by centrifugal force generated by the rotation of the rotor 7 and the magnetic attraction force of the stator 8 at the time of power generation. Thereby, a load is applied to the magnet 30A between the claw-like magnetic poles 23 and 24, whereby the magnet 30A may be distorted or broken.
A countermeasure against this is disclosed by Japanese Laid-open Patent Application No. 11-136913. In this publication, a magnet 30B is formed as shown in FIG. 19 and FIG. 20. That is, the magnet 30B is fixed to each of the claw-like magnetic poles 23 and 24 in such a manner that it covers the inner face 23a or 24a and the side faces 23c or 24c of the claw-like magnetic pole 23 or 24. A space 25 is formed between adjacent magnets 30B. Thereby, a set of the claw-like magnetic pole 23 and the magnet 30B and a set of the claw-like magnetic pole 24 and the magnet 30B move independently, thereby preventing the application of a load to the magnet 30B and the breakage of the magnet 30B.